1. Field of the Invention
The present invention relates to a lithium battery provided with a positive electrode, a negative electrode, a non-aqueous electrolyte, and a battery separator separating the above-mentioned positive electrode and negative electrode in a battery case, and battery polymeric materials employed for a battery separator separating the positive electrode and the negative electrode and a battery insulating packing sealing the battery case in a lithium battery. More particularly, the present invention is characterized in that discharge characteristics and the like of a lithium battery are prevented from being degrade even when the lithium battery is exposed to high temperature conditions, such as when the lithium battery is put into a reflowing furnace to be automatically soft-soldered.
2. Description of the Related Art
In recent years, a lithium battery employing a non-aqueous electrolyte to utilize oxidation and reduction of lithium ions have begun to be used as one of new-type lithium batteries having high power and high energy density.
Such a lithium battery employs the non-aqueous electrolyte as described above, and thereby evolution of hydrogen and oxygen due to a positive electrode and a negative electrode reacting during storage is restrained. Therefore, the lithium battery has begun to be used as an electric source for emergency such as for memory-backup and the like.
In the above-mentioned lithium battery, a positive electrode, a negative electrode and a non-aqueous electrolyte are generally contained in a battery case. In the lithium battery as described above, polymeric materials are employed for a battery separator separating the positive electrode and the negative electrode and a battery insulating packing electrically separating the battery case.
Further, in employing the lithium battery as an electric source for emergency such as for memory-backup and the like as described above, it is attempted that the lithium battery is put into a reflowing furnace to automatically soft-solder a lead terminal thereof onto a printed board.
When the lithium battery is put into a reflowing furnace to automatically soft-solder the lead terminal thereof onto the printed board as described above, the lithium battery is exposed to high temperature in the reflowing furnace and is usually kept under the high temperature conditions of 250xc2x0 C. for about ten seconds.
However, when the lithium battery is kept under high temperature conditions of 250xc2x0 C. for about ten seconds as described above, there exists a problem that the non-aqueous electrolyte in the battery case of the lithium battery reacts with the above-mentioned battery separator and the battery insulating packing which are formed by polymeric materials, whereby various performances of the lithium battery such as discharge capacity and the like are degraded.
An object of the present invention is to restrain polymeric materials as a battery separator separating a positive electrode and a negative electrode and a battery insulating packing sealing a battery case from reacting with a non-aqueous electrolyte in order to prevent various performances of a lithium battery such as discharge capacity and the like when the lithium battery is exposed to high temperature conditions such as when the lithium battery is put into a reflowing furnace to be automatically soft-soldered.
The first battery polymeric material according to the present invention employed for the battery separator and the battery insulating packing comprises repeating units wherein p-phenylene is combined with one type of group selected from the group composed of oxygen, a methylene group, an isopropylidene group, a carbonyl group, a carbonyldioxy group, a carboxylic acid anhydride group, an amide group, an ureylene group and a sulfonyl group.
Further, the second battery polymeric material according to the present invention employed for the battery separator and the battery insulating packing in the lithium battery comprises repeating units wherein at least two types of p-phenylene which is combined with one type of group selected from the group composed of oxygen, a methylene group, an isopropylidene group, a carbonyl group, a carbonyldioxy group, a carboxylic acid anhydride group, an amide group, an ureylene group, a sulfonyl group, sulfur and a carbonyloxy group are combined with each other.
Further, when the battery separator and the battery insulating packing in the lithium battery comprises the above-mentioned first and second polymeric materials, in the case where the lithium battery is exposed to the high temperature conditions such as the case where the lithium battery is put into a reflowing furnace to be automatically soft-soldered, the battery separator and the battery insulating packing which are formed by the above-mentioned polymeric materials are restrained from reacting with the non-aqueous electrolyte, and as a result, various performances of the lithium battery such as discharge capacity and the like are prevented from being degraded.
In the above-mentioned first battery polymeric material, it is preferable that the group combined with p-phenylene is composed of oxygen or a carbonyl group. On the other hand, in the above-mentioned second battery polymeric material, it is preferable that the groups combined with p-phenylene are composed of oxygen and a carbonyl group. Further, when the first and second battery polymeric material as described above are employed for the battery separator and the battery insulating packing of the lithium battery, in the case where the lithium battery is exposed to the high temperature conditions, the polymeric materials are further restrained from reacting with the non-aqueous electrolyte, and thereby discharge capacity of the lithium battery is further prevented from being degraded.
Further, the lithium battery according to the present invention is characterized in that the above-mentioned first and second battery polymeric materials are employed for the battery separator and the battery insulating packing of the lithium battery. The type of solvent and solute to be used for the non-aqueous electrolyte of the lithium battery and the type of materials to be used for the positive electrode and the negative electrode and the like are not particularly limited, that is, a solvent, a solute and materials which have been generally used in lithium batteries may be used. Additionally, the lithium battery according to the present invention may be either of a primary battery and a secondary battery.
In the lithium battery according to the present invention, examples of a solute to be used in the non-aqueous electrolyte include a lithium compound such as hexafluorophosphoric acid lithium (LiPF6), tetrafluoroboric acid lithium (LiBF4), trifluoro-methanesulfonic acid lithium (LiCF3SO3), lithium trifluoro-methanesulfonic acid imide [LiN(CF3SO2, )2], lithium pentafluoro-ethanesulfonic acid imide [LiN(C2F5SO2)2], lithium trifluoro-ethanesulfonic acid methide [LiC(CF3SO2)3], and the like.
Further, as a solvent to be used in the non-aqueous electrolyte, a solvent having a high permittivity such as ethylene carbonate, propylene carbonate, 1.2-buthylene carbonate, vinylene carbonate, xcex3-butyrolactone, sulfolane, and the like, or a solvent having a low viscosity such as 1.2-dimethoxyethane, 1.2-diethoxyethane, 1.2-etoxymethoxyethane, tetrahydrofuran, 1.3-dioxolane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like may be employed alone or in combination with not less than two types. In particular, when a mixture solvent of the above-mentioned solvent having a high permittivity and a low viscosity is employed, ion conductivity of the non-aqueous electrolyte is increased. Increasingly, when an alloy of lithium and aluminum is employed for the negative electrode, a coating layer excellent in ion conductivity is formed on the negative electrode, whereby discharge characteristics of the lithium battery is improved.
Further, in the lithium battery according to the present invention, examples of a positive electrode material to form the positive electrode include manganese dioxide, vanadium pentoxide, niobium oxide, cobalt-lithium oxide, nickel-lithium oxide and spinal manganese oxide, and the like. In particular, when boron-containing lithium-manganese complex oxide having boron or a boron compound dissolved therein is employed as the positive electrode material, the lithium battery excellent in charge/discharge cycle performance can be obtained.
Further, in the lithium battery according to the present invention, examples of a negative electrode material to form the negative electrode include a lithium alloy such as metal lithium, a lithium-aluminum alloy, a lithium-aluminum-manganese alloy, a lithium-lead alloy, a lithium-tin alloy, a lithium-silicon alloy and the like, graphite capable of occuluding and discharging of lithium ions, coke, a carbon material such as a calcined product of organic substances, and the like. In particular, when a Lixe2x80x94Al alloy is employed as described above, a coating layer excellent in ion conductivity is formed on the negative electrode due to the combination of the Lixe2x80x94Al alloy and a solvent in the non-aqueous electrolyte, whereby lithium batteries excellent in discharge characteristics can be obtained.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiment of the invention.